1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly, to a liquid crystal display device having variable viewing angles.
2. Discussion of the Related Art
Cathode ray tubes (CRTs) have been widely used as a display devices for televisions and a computer monitors. However, the cathode ray tube has a large size, heavy weight, and high driving voltage. Therefore, flat panel displays, being thin, light weight, and low in power consumption are increasing in demand. Thus, thin film transistor liquid crystal display (TFT-LCD) devices having good image reproduction and reduced thickness have been developed. In addition, LCD devices have gradually grown large in display area.
In general, a liquid crystal display (LCD) device includes two substrates, which are spaced apart and facing each other, and a liquid crystal layer interposed between the two substrates. Each of the substrates includes an electrode, and the electrodes of each substrate are also facing each other. Voltage is applied to each electrode, and thus an electric field is induced between the electrodes. Alignment of the liquid crystal molecules is changed by the varying intensity or direction of the electric field. The LCD device displays a picture by varying transmissivity of the light varying according to the arrangement of the liquid crystal molecules.
A conventional LCD device will be described hereinafter in detail with reference to figures.
FIG. 1 is an exploded perspective view illustrating a conventional LCD device. As shown in FIG. 1, the conventional LCD device 11 has upper and lower substrates 5 and 22, which are spaced apart from and facing each other, and also has liquid crystal 14 interposed between the upper substrate 5 and the lower substrate 22.
The upper substrate 5 includes a black matrix 6, a color filter layer 7, and a common electrode 18 subsequently on the inside (i.e., the side facing the lower substrate 22). The black matrix 6 has an opening. The color filter layer 7 corresponds to openings in the black matrix 6 and includes three sub-color filters of red (R), green (G), and blue (B). The common electrode 18 is formed on the color filter 7 and is transparent.
At least one gate line 13 and at least one data line 15 are formed on the inner surface of the lower substrate 22 (i.e., the side facing the upper substrate 5). The gate line 13 and the date line 15 cross each other to define a pixel area P. A thin film transistor T, as a switching element, is formed at the crossing of the gate line 13 and the data line 15. The thin film transistor T includes a gate electrode, a source electrode and a drain electrode. A plurality of such thin film transistors is arranged in a matrix form to correspond to other crossings of gate and data lines 13 and 15. A pixel electrode 17, which is connected to the thin film transistor T, is formed in the pixel area P. The pixel electrode 17 corresponds to the sub-pixel color filter, and is made of a transparent conductive material such as indium-tin-oxide (ITO) that transmits light. The lower substrate 22, which includes the thin film transistors T and the pixel electrodes 17 arranged in the matrix form may be commonly referred to as an array substrate.
Although not shown in the figure, the LCD device further includes a backlight as a light source and a printed circuit board (PCB) including driver integrated circuits (ICs) as a driving element. The upper substrate 5 and the lower substrate 22 having the liquid crystal layer 14 therebetween may be commonly referred to as a liquid crystal cell or as a liquid crystal panel.
A liquid crystal (LC) cell having twisted nematic (TN) mode is widely used. Liquid crystal molecules in the TN mode LC cell have rod shapes that are thin and long and that are helically twisted such that long axes of the liquid crystal molecules are progressively changed, having a uniform pitch.
In the TN mode, incident polarized light has different characteristics of viewing angles according to arrangements of long axes and short axes of the liquid crystal molecules. That is, viewing angles of the LCD device are made along the long axes of the liquid crystal molecules having a helical structure, and thus the viewing angles are varied depending on a viewing direction.
Generally, the liquid crystal display device has a symmetric horizontal viewing angle range of about +45 degrees to about −45 degrees and a vertical viewing angle range of about −15 degrees to about +15 degrees. Accordingly, images may be easily distorted in the vertical direction as the viewing angles get narrow.
In the case of small size LCD devices, the display is seen from limited angles by a few users. As LCD displays grow larger, the LCD device may be watched from a wider variety of angles by a lot of users at the same time. In these situations, the narrow viewing angles of the LCD device may cause problems.
To overcome the limited viewing angles of the LCD device, various modes, such as a film-compensated mode, a multi-domain mode, an in-plane switching (IPS) mode, and so forth, have been proposed. In the film-compensated mode, a compensating film or a diffusing film may be used. In the multi-domain mode, a pixel is divided into several domains and one domain has an arrangement direction different from other domains, thereby compensating the viewing angle. In the IPS mode, two electrodes for driving LC molecules are disposed on one substrate, whereby an electric field is induced in plane.
However, the LCD device has only a wide viewing angle mode, and the viewing angle mode cannot be changed according to circumstances, for example, a display for a cash dispenser of a bank that requires security.